1. Field of the Invention
The present invention relates to a satellite communication receiving apparatus, and in particular to a satellite communication receiving apparatus capable of receiving a satellite communication broadcasting using an L-band and a Phase Shift Keying(PSK) by sharing a temperature compensation voltage control oscillator with a voltage control oscillator used in Costas-loop and a local oscillator used in an intermediate frequency apparatus, thereby securing effective satellite communication broadcasting receiving and facilitating a simplification thereof.
2. Description of the Conventional Art
Conventionally, a satellite communication receiving apparatus using a L-band phase shift keying method, as shown in FIG. 2, includes an L-band receiving antenna 100 for receiving satellite communication broadcasting signals from a satellite; a Low Noise Amplifier(LNA) 101 for facilitating the frequency of the satellite communication signals from the antenna 100 to be a predetermined level without undesired noises; a first amplifier 102 for amplifying the satellite communication signals up to a predetermined level, in which the frequency is converted at the low noise amplifier 101; a first band filter 103 for filtering all bands of the signals amplified at the first amplifier 102; a second amplifier 104 for amplifying all band signals filtered at the first band filter 103; a modulator 105 for generating an intermediate frequency by mixing the signals amplified at the second amplifier 104 with the local oscillating frequency, respectively, for a 90.degree. phase keying; and a demodulator 112 for modulating the intermediate frequency signals keyed at the modulator 105 and for obtaining data from the keyed signals.
The modulator 105 includes a temperature compensating oscillator 111 for oscillating a base frequency; a first to third intermediate frequency generator 106 to 108 for sequentially generating intermediate frequencies by mixing the local oscillating frequency generated in response to the base frequency from the temperature compensating oscillator 111 and the signals inputted from the second amplifier 104; a gain control amplifier 109 for outputting the level changes of the intermediate frequency signals outputted from the third intermediate frequency generator 108; and a sixth amplifier 110 for amplifying the intermediate frequency signals amplified at the gain control amplifier 109 to a predetermined level and for transferring the amplified signals to the demodulator 112.
The first intermediate frequency generator 106 included a first phase synchronous loop circuit 106a for generating a local oscillating frequency by the base frequency oscillated from the temperature compensating oscillator 111; a first mixer 106b for mixing the local oscillating frequency generated at the first phase synchronous loop circuit 106a and the satellite broadcasting signals from the second amplifier 104; a second band filter 106c for filtering the output signals of the first mixer 106b; and a third amplifier 106d for amplifying the band signals filtered at the second band filter 106c and for inputting the amplified signals into the second intermediate frequency generator 107.
The third amplifier 106d consisted of a second phase synchronous loop circuit 107a, a second mixer 107b, a third band filter 107 and a fourth amplifier 107d, the same as the first intermediate frequency generator 106.
In addition, the third intermediate frequency generator 108 consisted of a third phase synchronous loop circuit 108a, a third mixer 108b, a fourth band filter 108c and a fifth amplifier 108d, the same as the first and second intermediate frequency generators 106 and 107.
The modulator 112 consisted of a Costas loop circuit 113 for keying the intermediate frequency keyed at the modulator 105 and a sampling circuit 114 for outputting the signals outputted from the Costas loop circuit 113.
The Costas loop circuit 113 includes a first and second phase detection circuits 113a and 113b for keying the signals from the sixth amplifier 110 of the modulator 105; first and second low band filters 113d and 113i for respectively passing the frequency lower than the cut frequency from the output of the first and second phase detection circuits 113a and 113b; a multiplier 113e for outputting the value in proportion to the multiplication of the two input signals passed from the first and second low band filters 113d and 113i; a third low band filter 113f for filtering the output signals of the multiplier 113e; an integrator 113g for outputting the integrated value in proportion to the signals filtered at the third low band filter 113f; a voltage control oscillator 113h for oscillating the control voltage oscillating frequency by the integrated value outputted at the integrator 113g and for inputting the oscillated frequency into the first phase detection circuit 113a; and a 90.degree. shifter 113c for shifting the output signals of the voltage control oscillator 113h by 90.degree. and sending the shifted signals to the second phase detection circuit 113b.
In addition, the sampling circuit 114 includes a comparator 114a for separating the analog signal wave modulated through the second low filter 113i into a plus voltage and a minus voltage and a clock generator 114b for sampling the signals inputted from the second low band filter 113i in response to the value inputted from the comparator 114a.
As described above, the conventional satellite communication receiving apparatus using the L-band phase shift keying method is directed to convert the satellite communication signals received from the L-band receiving antenna 100 into a predetermined level through the low noise amplifier 101 which signals are amplified through the first amplifier 102 and filtered through the first band filter 103.
The satellite broadcasting signals filtered through the first band filter 103 are amplified and outputted through the second amplifier 104.
The signals amplified through the second amplifier 104 are mixed through the first mixer 106b with the frequencies oscillated by the temperature compensating oscillator 111 and the first phase synchronous loop circuit 106a of the first intermediate frequency generator 106, filtered through the second band filter 106c, amplified through the third amplifier 106d, and inputted into the second intermediate frequency generator 107. The signals outputted from the third amplifier 106d are sequentially inputted into the second intermediate frequency generator 107 and the third intermediate frequency generator 108.
The third intermediate frequency is compensated for input level changes through the gain control amplifier 109, amplified through the sixth amplifier 110 and inputted into the modulator 112.
At this time, if the signal inputted therefrom is X1, X1, filtered at the first low band filter 113d through the second phase detection circuit 113b is inputted into the multiplier 113e. Then, if the signal inputted into the multiplier 113e is X3, a signal at the multiplier 113e in proportion to the input two signals is outputted therefrom.
The signals are filtered through the third low band filter 113f, integrated through the integrator 113g, and inputted into the voltage control oscillator 113h.
The voltage control oscillator 113h outputs the oscillating frequency in response to the control voltage Vt and inputs the frequency into the first and second phase detection circuits 113a and 113b in a 90.degree. shifted form.
The signals outputted at the Costa loop circuit 113 are inputted into the clock generator 114b and the sampling circuit 114, of which one part thereof is inputted in an inputted state and the other part of thereof is inputted through a comparator 114a as the signals needed in generating the clocks at the clock generating circuit 114b.
The clock generating circuit 114b modulates the signals received from the antenna 100 for the digital signals.
However, since the conventional satellite communication receiving apparatus using the L-band phase shift keying method utilizes the multi-phases of the mixer in order to modulate the signals of the L-band phase shift keying, generates the third intermediate frequency at the third intermediate frequency generator, and modulates the desired digital data from the third intermediate frequency, a plurality of band filter, mixer, phase synchronous loop circuits and temperature compensating oscillating circuits for the base oscillating frequency are additionally needed, thereby causing a relatively complicated design process and undesired repetitive parts.